Process to Recover Alcohol with Reduced Water From Overhead of Acid Column

ABSTRACT

A process for recovering ethanol obtained from the hydrogenation of acetic acid. The crude ethanol product is separated in a column to produce a distillate stream comprising acetaldehyde and ethyl acetate and a residue stream comprising ethanol, acetic acid, ethyl acetate and water. The ethanol product is recovered from the residue stream.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.13/094,588, filed on Apr. 26, 2011, and U.S. application Ser. No.13/292,914, filed on Nov. 9, 2011, the entire contents and disclosuresof which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to processes for producingalcohol and, in particular, to a process for recovering ethanol withreduced water.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from organic feedstocks, such as petroleum oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosicmaterials, such as corn or sugar cane. Conventional methods forproducing ethanol from organic feed stocks, as well as from cellulosicmaterials, include the acid-catalyzed hydration of ethylene, methanolhomologation, direct alcohol synthesis, and Fischer-Tropsch synthesis.Instability in organic feed stock prices contributes to fluctuations inthe cost of conventionally produced ethanol, making the need foralternative sources of ethanol production all the greater when feedstock prices rise. Starchy materials, as well as cellulosic materials,are converted to ethanol by fermentation. However, fermentation istypically used for consumer production of ethanol, which is suitable forfuels or human consumption. In addition, fermentation of starchy orcellulosic materials competes with food sources and places restraints onthe amount of ethanol that can be produced for industrial use.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. During the reduction of alkanoicacids, e.g., acetic acid, other compounds are formed with ethanol or areformed in side reactions. These impurities limit the production andrecovery of ethanol from such reaction mixtures. For example, duringhydrogenation, esters are produced that together with ethanol and/orwater form azeotropes, which are difficult to separate. In addition,when conversion is incomplete, acid remains in the crude ethanolproduct, which must be removed to recover ethanol.

EP02060553 describes a process for converting hydrocarbons to ethanolinvolving converting the hydrocarbons to ethanoic acid and hydrogenatingthe ethanoic acid to ethanol. The stream from the hydrogenation reactoris separated to obtain an ethanol stream and a stream of acetic acid andethyl acetate, which is recycled to the hydrogenation reactor.

U.S. Pat. No. 7,842,844 describes a process for improving selectivityand catalyst activity and operating life for the conversion ofhydrocarbons to ethanol and optionally acetic acid in the presence of aparticulate catalyst, said conversion proceeding via a syngas generationintermediate step.

The need remains for improved processes for recovering ethanol from acrude product obtained by reducing alkanoic acids, such as acetic acid,and/or other carbonyl group-containing compounds.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid in a reactorin the presence of a catalyst to form a crude ethanol product,separating a portion of the crude ethanol product in a firstdistillation column to yield a first distillate comprising acetaldehydeand ethyl acetate, and a first residue comprising ethanol, acetic acid,ethyl acetate and water, separating a portion of the first residue in asecond distillation column to yield a second residue comprising aceticacid and an overhead vapor comprising ethanol, ethyl acetate and water,removing water from at least a portion of the overhead vapor, preferablyat least 50% of the overhead vapor, to yield an ethanol mixture streamhaving a lower water content than the at least a portion of the overheadvapor, and separating at least a portion of the ethanol mixture streamin a third distillation column to yield a third distillate comprisingethyl acetate and a third residue comprising ethanol and less than 8 wt.% water, e.g., less than 3 wt. % water or less than 0.5 wt. % water. Inone embodiment, water is removed from the overhead vapor using a waterseparator selected from the group consisting of an adsorption unit,membrane, extractive column distillation, molecular sieves, andcombinations thereof.

In a second embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid in a reactorin the presence of a catalyst to form a crude ethanol product,separating a portion of the crude ethanol product in a firstdistillation column to yield a first distillate comprising acetaldehydeand ethyl acetate, and a first residue comprising ethanol, acetic acid,and water, separating a portion of the first residue in a seconddistillation column to yield a second residue comprising acetic acid andwater, and an overhead vapor comprising ethanol and water, wherein aweight majority of the water fed to the second column is removed in thesecond residue, and removing water from at least a portion of theoverhead vapor to yield an ethanol product having less than 8 wt. %water, e.g., less than 3 wt. % water or less than 0.5 wt. % water.

In a third embodiment, the present invention is directed to a processfor producing ethanol, comprising providing a crude ethanol product,separating a portion of the crude ethanol product in a firstdistillation column to yield a first distillate comprising acetaldehydeand ethyl acetate, and a first residue comprising ethanol, acetic acid,ethyl acetate and water, separating a portion of the first residue in asecond distillation column to yield a second residue comprising aceticacid and an overhead vapor comprising ethanol, ethyl acetate and water,removing water from at least a portion of the overhead vapor, preferablyat least 50% of the overhead vapor, to yield an ethanol mixture streamhaving a lower water content than the at least a portion of the overheadvapor, and separating at least a portion of the ethanol mixture streamin a third distillation column to yield a third distillate comprisingethyl acetate and a third residue comprising ethanol and less than 8 wt.% water, e.g., less than 3 wt. % water or less than 0.5 wt. % water. Inone embodiment, water is removed from the overhead vapor using a waterseparator selected from the group consisting of an adsorption unit,membrane, extractive column distillation, molecular sieves, andcombinations thereof.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, wherein like numeralsdesignate similar parts.

FIG. 1 is a schematic diagram of an ethanol production system withmultiple distillation columns to recover ethanol including an acidcolumn and water separator in accordance with one embodiment of thepresent invention.

FIG. 2 is a schematic diagram of an ethanol production system withmultiple distillation columns having an extractive distillation forrecovering ethanol from a stream being recycled to the reactor inaccordance with one embodiment of the present invention.

FIG. 3 is a schematic diagram of an ethanol production system withmultiple distillation columns to recover ethanol including an acidcolumn and vapor esterification unit in accordance with one embodimentof the present invention.

FIG. 4 is a schematic diagram of an ethanol production system withmultiple distillation columns having an extractive distillation forrecovering ethanol from a stream being recycled to the initial column inaccordance with one embodiment of the present invention.

FIG. 5 is a schematic diagram of an ethanol production system withmultiple distillation columns to recover ethanol from a stream thatcomprises acetic acid and low concentrations of ethyl acetate inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to processes for recovering ethanolproduced by hydrogenating acetic acid in the presence of a catalyst. Thehydrogenation reaction produces a crude ethanol product that comprisesethanol, water, ethyl acetate, acetaldehyde, acetic acid, and otherimpurities. Water is co-produced with ethanol in the hydrogenationreaction in about a 1:1 molar ratio, and thus producing ethanol alsoresults in the production of water. This makes recovering industrialgrade ethanol or fuel grade ethanol difficult due to the excess water.In some embodiments, the processes of the present invention involveseparating the crude ethanol product in a first column into a residuestream comprising ethanol, water, ethyl acetate and/or acetic acid and adistillate stream comprising acetaldehyde and ethyl acetate. The firstcolumn primarily removes light organics in the distillate and returnsthose organics to the reactor for subsequent hydrogenation.Subsequently, the ethanol is removed from the residue stream to yield anethanol product. Advantageously, this separation approach results inreducing energy requirements to recover ethanol, in particular anhydrousethanol for fuel grade ethanol, from the crude ethanol product.

In recovering ethanol, the processes of the present invention use one ormore distillation columns. In preferred embodiments, the residue streamfrom in the initial column, e.g., first column, comprises a substantialportion of the ethanol, water and acetic acid from the crude ethanolproduct. The residue stream, for example, may comprise at least 50% ofthe ethanol from the crude ethanol product, and more preferably at least70%. In terms of ranges, the residue stream may comprise from 50% to99.9% of the ethanol from the crude ethanol product, and more preferablyfrom 70% to 99%. Preferably, the amount of ethanol from the crudeethanol product recovered in the residue may be greater than 97.5%, e.g.greater than 99%.

Depending on the ethyl acetate concentration in the residue and whetherin situ esterification occurs in the residue or in an esterificationreactor, it may be necessary to further separate the ethyl acetate andethanol in a separate column. Preferably, this separate column islocated after the water has been removed using a distillation column andwater separator. Generally, a separate column may be necessary when theresidue comprises at least 50 wppm ethyl acetate or esterification wouldbe expected to occur. When the residue comprises less than 50 wppm ethylacetate, it may not be necessary to use a separate column to separateethyl acetate and ethanol.

In preferred embodiments, the residue stream comprises a substantialportion of the water and acetic acid from the crude ethanol product. Theresidue stream may comprise at least 80% of the water from the crudeethanol product, and more preferably at least 90%. In terms of ranges,the residue stream preferably comprises from 80% to 100% of the waterfrom the crude ethanol product, and more preferably from 90% to 99.4%.The residue stream may comprise at least 85% of the acetic acid from thecrude ethanol product, e.g., at least 90% and more preferably about100%. In terms of ranges, the residue stream preferably comprises from85% to 100% of the acetic acid from the crude ethanol product, and morepreferably from 90% to 100%. In one embodiment, substantially all of theacetic acid is recovered in the residue stream.

The residue stream, which comprises ethanol, ethyl acetate, water, andacetic acid, may be further separated to recover ethanol. Because thesecompounds may not be in equilibrium, additional ethyl acetate may beproduced through esterification of ethanol and acetic acid. In onepreferred embodiment, the water and acetic acid may be removed asanother residue stream in a separate distillation column. In addition,the water carried over in the separate distillation column may beremoved with a water separator that is selected from the groupconsisting of an adsorption unit, membrane, extractive columndistillation, molecular sieves, or a combination thereof.

In one embodiment each of the columns is sized to be capital andeconomically feasible for the rate of ethanol production. The totaldiameter for the columns used to separate the crude ethanol product maybe from 5 to 40 meters, e.g., from 10 to 30 meters or from 12 to 20meters. Each column may have a varying size. In one embodiment, theratio of column diameter in meters for all the distillation columns totons of ethanol produced per hour is from 1:2 to 1:30, e.g., from 1:3 to1:20 or from 1:4 to 1:10. This would allow the process to achieveproduction rates of 25 to 250 tons of ethanol per hour.

The distillate from the initial column comprises light organics, such asacetaldehyde, diethyl acetal, acetone, and ethyl acetate. As a result,the initial column provides an efficient means for removing acetaldehydeand ethyl acetate. In addition, minor amounts of ethanol and water maybe present in the distillate. In addition, acetaldehyde, diethyl acetal,and acetone are not carried over with the ethanol when multiple columnsare used, thus reducing the formation of byproducts from acetaldehyde,diethyl acetal, and acetone. In particular, acetaldehyde and/or ethylacetate may be returned to the reactor and converted to additionalethanol. In another embodiment, a purge may remove these light organicsfrom the system.

In one embodiment, the residue from the initial column comprises ethylacetate. Although ethyl acetate is also partially withdrawn into thefirst distillate, a higher ethyl acetate concentration in the firstresidue advantageously leads to increased ethanol concentration in thefirst residue and decreased ethanol concentrations in the firstdistillate. Thus overall ethanol recovery may be increased. Ethylacetate may be separated from ethanol in a separate column near the endof the purification process. In removing ethyl acetate, additional lightorganics may also be removed and thus improve the quality of the ethanolproduct by decreasing impurities. Preferably, water and/or acetic acidmay be removed prior to the ethyl acetate/ethanol separation.

In one embodiment, after the ethyl acetate is separated from ethanoldownstream of the initial column, the ethyl acetate is returned to theinitial column and fed near the top of that column. This allows for anyethanol removed with the ethyl acetate to be recovered and furtherreduces the amount of ethanol being recycled to the reactor. Decreasingthe amount of ethanol recycled to the reactor may reduce reactor capitaland improve efficiency in recovering ethanol. Preferably, the ethylacetate is removed in the distillate of the first column and returned tothe reactor with the acetaldehyde.

The processes of the present invention may be used with anyhydrogenation process for producing ethanol. The materials, catalysts,reaction conditions, and separation processes that may be used in thehydrogenation of acetic acid are described further below.

The raw materials, acetic acid and hydrogen, used in connection with theprocess of this invention may be derived from any suitable sourceincluding natural gas, petroleum, coal, biomass, and so forth. Asexamples, acetic acid may be produced via methanol carbonylation,acetaldehyde oxidation, ethane oxidation, oxidative fermentation, andanaerobic fermentation. Methanol carbonylation processes suitable forproduction of acetic acid are described in U.S. Pat. Nos. 7,208,624;7,115,772; 7,005,541; 6,657,078; 6,627,770; 6,143,930; 5,599,976;5,144,068; 5,026,908; 5,001,259; and 4,994,608, the entire disclosuresof which are incorporated herein by reference. Optionally, theproduction of ethanol may be integrated with such methanol carbonylationprocesses.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from other carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from other available carbonsources. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process may be derivedpartially or entirely from syngas. For example, the acetic acid may beformed from methanol and carbon monoxide, both of which may be derivedfrom syngas. The syngas may be formed by partial oxidation reforming orsteam reforming, and the carbon monoxide may be separated from syngas.Similarly, hydrogen that is used in the step of hydrogenating the aceticacid to form the crude ethanol product may be separated from syngas. Thesyngas, in turn, may be derived from a variety of carbon sources. Thecarbon source, for example, may be selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.Syngas or hydrogen may also be obtained from bio-derived methane gas,such as bio-derived methane gas produced by landfills or agriculturalwaste.

Biomass-derived syngas has a detectable ¹⁴C isotope content as comparedto fossil fuels such as coal or natural gas. An equilibrium forms in theEarth's atmosphere between constant new formation and constantdegradation, and so the proportion of the ¹⁴C nuclei in the carbon inthe atmosphere on Earth is constant over long periods. The samedistribution ratio n¹⁴C:n¹²C ratio is established in living organisms asis present in the surrounding atmosphere, which stops at death and ¹⁴Cdecomposes at a half life of about 6000 years. Methanol, acetic acidand/or ethanol formed from biomass-derived syngas would be expected tohave a ¹⁴C content that is substantially similar to living organisms.For example, the 14C:¹²C ratio of the methanol, acetic acid and/orethanol may be from one half to about 1 of the 14C:¹²C ratio for livingorganisms. In other embodiments, the syngas, methanol, acetic acidand/or ethanol described herein are derived wholly from fossil fuels,i.e. carbon sources produced over 60,000 years ago, may have nodetectable ¹⁴C content.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteriodes, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodesamylophilus and Bacteriodes ruminicola. Optionally, in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. No. 6,509,180, and U.S.Pub. Nos. 2008/0193989 and 2009/0281354, the entireties of which areincorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. Another biomass source is black liquor, which is anaqueous solution of lignin residues, hemicellulose, and inorganicchemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by converting carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form syngas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into synthesis gas, andU.S. Pat. No. 6,685,754, which discloses a method for the production ofa hydrogen-containing gas composition, such as a synthesis gas includinghydrogen and carbon monoxide, are incorporated herein by reference intheir entireties.

Acetic acid fed to the hydrogenation reactor may also comprise othercarboxylic acids and anhydrides, as well as acetaldehyde and acetone.Preferably, a suitable acetic acid feed stream comprises one or more ofthe compounds selected from the group consisting of acetic acid, aceticanhydride, acetaldehyde, ethyl acetate, and mixtures thereof. Theseother compounds may also be hydrogenated in the processes of the presentinvention. In some embodiments, the presence of carboxylic acids, suchas propanoic acid, or propanal, may be beneficial in producing propanol.Water may also be present in the acetic acid feed.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the ethanol synthesis reaction zones of thepresent invention without the need for condensing the acetic acid andlight ends or removing water, saving overall processing costs.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid may be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment, the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is mixed with other gases before vaporizing,followed by heating the mixed vapors up to the reactor inlettemperature. Preferably, the acetic acid is transferred to the vaporstate by passing hydrogen and/or recycle gas through the acetic acid ata temperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

Some embodiments of the process of hydrogenating acetic acid to formethanol may include a variety of configurations using a fixed bedreactor or a fluidized bed reactor. In many embodiments of the presentinvention, an “adiabatic” reactor can be used; that is, there is littleor no need for internal plumbing through the reaction zone to add orremove heat. In other embodiments, a radial flow reactor or reactors maybe employed, or a series of reactors may be employed with or withoutheat exchange, quenching, or introduction of additional feed material.Alternatively, a shell and tube reactor provided with a heat transfermedium may be used. In many cases, the reaction zone may be housed in asingle vessel or in a series of vessels with heat exchangerstherebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably, the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may rangefrom 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to300° C., or from 250° C. to 300° C. The reactor pressure may range from100 kPa to 4500 kPa, e.g., from 150 kPa to 3500 kPa, or from 500 kPa to3000 kPa. The reactants may be fed to the reactor at a gas hourly spacevelocity (GHSV) from 50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500 hr⁻¹ to30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to 6500hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 18:1 to 2:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature, andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,from 0.1 to 100 seconds.

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst. Exemplary catalysts arefurther described in U.S. Pat. Nos. 7,608,744 and 7,863,489, and U.S.Pub. Nos. 2010/0121114 and 2010/0197985, the entireties of which areincorporated herein by reference. In another embodiment, the catalystcomprises a Co/Mo/S catalyst of the type described in U.S. Pub. No.2009/0069609, the entirety of which is incorporated herein by reference.In some embodiments, the catalyst may be a bulk catalyst.

In one embodiment, the catalyst comprises a first metal selected fromthe group consisting of copper, iron, cobalt, nickel, ruthenium,rhodium, palladium, osmium, iridium, platinum, titanium, zinc, chromium,rhenium, molybdenum, and tungsten. Preferably, the first metal isselected from the group consisting of platinum, palladium, cobalt,nickel, and ruthenium.

As indicated above, in some embodiments, the catalyst further comprisesa second metal, which typically would function as a promoter. Ifpresent, the second metal preferably is selected from the groupconsisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. More preferably, the second metal is selectedfrom the group consisting of copper, tin, cobalt, rhenium, and nickel.

In certain embodiments where the catalyst includes two or more metals,e.g., a first metal and a second metal, the first metal preferably ispresent in the catalyst in an amount from 0.1 to 10 wt. %, e.g., from0.1 to 5 wt. %, or from 0.1 to 3 wt. %. The second metal preferably ispresent in an amount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %,or from 0.1 to 7.5 wt. %.

Preferred metal combinations for exemplary catalyst compositions includeplatinum/tin, platinum/ruthenium, platinum/rhenium, palladium/ruthenium,palladium/rhenium, cobalt/palladium, cobalt/platinum, cobalt/chromium,cobalt/ruthenium, cobalt/tin, silver/palladium, copper/palladium,copper/zinc, nickel/palladium, gold/palladium, ruthenium/rhenium, orruthenium/iron.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin,and rhenium. When present, the total weight of the third metalpreferably is from 0.05 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from0.1 to 7.5 wt. %. In one embodiment, the catalyst may comprise platinum,tin and cobalt.

In addition to one or more metals, in some embodiments of the presentinvention the catalysts further comprise a support or a modifiedsupport. As used herein, the term “modified support” refers to a supportthat includes a support material and a support modifier, which adjuststhe acidity of the support material. The total weight of the support ormodified support, based on the total weight of the catalyst, preferablyis from 75 to 99.9 wt. %, e.g., from 78 to 99 wt. %, or from 80 to 97.5wt. %. Preferred supports include silicaceous supports, such as silica,silica/alumina, a Group IIA silicate such as calcium metasilicate,pyrogenic silica, high purity silica, and mixtures thereof. Othersupports may include, but are not limited to, iron oxide, alumina,titania, zirconia, magnesium oxide, carbon, graphite, high surface areagraphitized carbon, activated carbons, and mixtures thereof.

The support may be a modified support and the support modifier ispresent in an amount from 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %,from 1 to 20 wt. %, or from 3 to 15 wt. %, based on the total weight ofthe catalyst. In some embodiments, the support modifier may be an acidicmodifier that increases the acidity of the catalyst. Suitable acidicsupport modifiers may be selected from the group consisting of: oxidesof Group IVB metals, oxides of Group VB metals, oxides of Group VIBmetals, oxides of Group VIIB metals, oxides of Group VIIIB metals,aluminum oxides, and mixtures thereof. Acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,Al₂O₃, B₂O₃, P₂O₅, Sb₂O₃, WO₃, MoO₃, Fe₂O₃, Cr₂O₃, V₂O₅, MnO₂, CuO,Co₂O₃, and Bi₂O₃. Preferred support modifiers include oxides oftungsten, molybdenum, and vanadium.

In another embodiment, the support modifier may be a basic modifier thathas a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth metal oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. Thebasic support modifier may be selected from the group consisting ofoxides and metasilicates of any of sodium, potassium, magnesium,calcium, scandium, yttrium, and zinc, as well as mixtures of any of theforegoing. In one embodiment, the basic support modifier is a calciumsilicate, such as calcium metasilicate (CaSiO₃). The calciummetasilicate may be crystalline or amorphous.

Catalysts on a modified support may include one or more metals selectedfrom the group consisting of platinum, palladium, cobalt, tin, andrhenium on a silica support, optionally modified by one or moremodifiers selected from the group consisting of calcium metasilicate,and one or more oxides of tungsten, molybdenum, and/or vanadium.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. Nos. 7,608,744 and 7,863,489 and U.S. Pub. No. 2010/0197485referred to above, the entireties of which are incorporated herein byreference.

After the washing, drying and calcining of the catalyst is completed,the catalyst may be reduced in order to activate it. Reduction iscarried out in the presence of a reducing gas, preferably hydrogen. Thereducing gas is optionally continuously passed over the catalyst at aninitial ambient temperature that is increased up to 400° C. In oneembodiment, the reduction is carried out after the catalyst has beenloaded into the reaction vessel where the hydrogenation will be carriedout.

In particular, the hydrogenation of acetic acid may achieve favorableconversion of acetic acid and favorable selectivity and productivity toethanol. For purposes of the present invention, the term “conversion”refers to the amount of acetic acid in the feed that is converted to acompound other than acetic acid. Conversion is expressed as a percentagebased on acetic acid in the feed. The conversion may be at least 40%,e.g., at least 50%, at least 60%, at least 70% or at least 80%. Althoughcatalysts that have high conversions are desirable, such as at least 80%or at least 90%, in some embodiments a low conversion may be acceptableat high selectivity for ethanol. Selectivity is expressed as a molepercent based on converted acetic acid. It should be understood thateach compound converted from acetic acid has an independent selectivityand that selectivity is independent from conversion. For example, if 60mole % of the converted acetic acid is converted to ethanol, we refer tothe ethanol selectivity as 60%. Preferably, the catalyst selectivity toethanol is at least 60%, e.g., at least 70%, or at least 80%. Preferredembodiments of the hydrogenation process also have low selectivity toundesirable products, such as methane, ethane, and carbon dioxide. Theselectivity to these undesirable products preferably is less than 4%,e.g., less than 2% or less than 1%.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. The productivity may rangefrom 100 to 3,000 grams of ethanol per kilogram of catalyst per hour.

In various embodiments of the present invention, the crude ethanolproduct produced by the hydrogenation process, before any subsequentprocessing, such as purification and separation, will typically compriseacetic acid, ethanol and water. Exemplary compositional ranges for thecrude ethanol product are provided in Table 1, excluding hydrogen. The“others” identified in Table 1 may include, for example, esters, ethers,aldehydes, ketones, alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol   5 to 72  15 to 72 15 to 70  25 to 65 Acetic Acid   0 to 90   0 to 50   0 to 35   0 to 15Water   5 to 40   5 to 30  10 to 30  10 to 26 Ethyl Acetate   0 to 30  1 to 25   3 to 20   5 to 18 Acetaldehyde   0 to 10  0 to 3 0.1 to 3 0.2 to 2  Others 0.1 to 10 0.1 to 6  0.1 to 4  —

At higher conversions, the crude ethanol product of Table 1 may have lowconcentrations of acetic acid. The crude ethanol product may compriseacetic acid, for example, in an amount ranging from 0.01 wt. % to 20 wt.%, e.g., 0.05 wt. % to 15 wt. %, from 0.1 wt. % to 10 wt. % or from 1wt. % to 5 wt. %. In embodiments having lower amounts of acetic acid,the conversion of acetic acid is preferably greater than 75%, e.g.,greater than 85% or greater than 90%. In addition, the selectivity toethanol may also be preferably high, and is preferably greater than 75%,e.g., greater than 85% or greater than 90%.

Exemplary ethanol recovery systems in accordance with embodiments of thepresent invention are shown in FIGS. 1-5. Each hydrogenation system 100provides a suitable hydrogenation reactor and a process for separatingethanol from the crude reaction mixture according to an embodiment ofthe invention. System 100 comprises reaction zone 101 and separationzone 102. Further modifications and additional components to reactionzone 101 and separation zone 102 are described below.

As shown in FIGS. 1-5, the feed to reactor 103 comprises fresh aceticacid. Hydrogen and acetic acid are fed to vaporizer 104 via lines 105and 106, respectively, to create a vapor feed stream in line 107 that isdirected to reactor 103. In one embodiment, lines 105 and 106 may becombined and jointly fed to the vaporizer 104. The temperature of thevapor feed stream in line 107 is preferably from 100° C. to 350° C.,e.g., from 120° C. to 310° C. or from 150° C. to 300° C. Any feed thatis not vaporized is removed from vaporizer 104, via blowdown 108. Inaddition, although line 107 is shown as being directed to the top ofreactor 103, line 107 may be directed to the side, upper portion, orbottom of reactor 103.

Reactor 103 contains the catalyst that is used in the hydrogenation ofthe carboxylic acid, preferably acetic acid. In one embodiment, one ormore guard beds (not shown) may be used upstream of the reactor,optionally upstream of vaporizer 104, to protect the catalyst frompoisons or undesirable impurities contained in the feed orreturn/recycle streams. Such guard beds may be employed in the vapor orliquid streams. Suitable guard bed materials may include, for example,carbon, silica, alumina, ceramic, or resins. In one aspect, the guardbed media is functionalized, e.g., silver functionalized, to trapparticular species such as sulfur or halogens. During the hydrogenationprocess, a crude ethanol product is withdrawn, preferably continuously,from reactor 103 via line 109.

The crude ethanol product may be condensed and fed to a separator 110,which, in turn, forms a vapor stream 112 and a liquid stream 113. Insome embodiments, separator 110 may comprise a flasher or a knockoutpot. The separator 110 may operate at a temperature from 20° C. to 350°C., e.g., from 30° C. to 325° C. or from 60° C. to 250° C. The pressureof separator 110 may be from 100 kPa to 3000 kPa, e.g., from 125 kPa to2500 kPa or from 150 kPa to 2200 kPa. Optionally, the crude ethanolproduct in line 109 may pass through one or more membranes to separatehydrogen and/or other non-condensable gases.

Vapor stream 112 exiting separator 110 may comprise hydrogen andhydrocarbons, and may be purged and/or returned to reaction zone 101. Asshown, vapor stream 112 is combined with the hydrogen feed 105 andco-fed to vaporizer 104. In some embodiments, the returned vapor stream112 may be compressed before being combined with hydrogen feed 105.

Liquid stream 113 from separator 110 is withdrawn and directed as a feedcomposition to the side of first distillation column 115, also referredto as an “extractive column.” Liquid stream 113 may be heated fromambient temperature to a temperature of up to 70° C., e.g., up to 50°C., or up to 40° C. The additional energy required to pre-heat liquidstream 113 above 70° C. does not achieve the desired energy efficiencyin first column 115 with respect to reboiler duties.

In another embodiment, liquid stream 113 is not separately preheated,but is withdrawn from separator 110, and cooled if needed, at atemperature of less than 70° C., e.g., less than 50° C., or less than40° C., and directly fed to first column 115.

In one embodiment, the contents of liquid stream 113 are substantiallysimilar to the crude ethanol product obtained from the reactor, exceptthat the composition has been depleted of hydrogen, carbon dioxide,methane and/or ethane, which have been removed by separator 110.Accordingly, liquid stream 113 may also be referred to as a crudeethanol product. Exemplary components of liquid stream 113 are providedin Table 2. It should be understood that liquid stream 113 may containother components, not listed in Table 2.

TABLE 2 FEED COMPOSITION TO COLUMN 115 (Liquid Stream 113) Conc. (wt. %)Conc. (wt. %) Conc. (wt. %) Ethanol 5 to 72 10 to 70 15 to 65 AceticAcid <90  5 to 80  0 to 35 Water 5 to 40  5 to 30 10 to 26 Ethyl Acetate<30  1 to 25  3 to 20 Acetaldehyde <10 0.001 to 3    0.1 to 3   Acetal<5 0.01 to 5   0.01 to 3   Acetone <5 0.0005 to 0.05  0.001 to 0.03 

The amounts indicated as less than (<) in the tables throughout thepresent specification are preferably not present and if present may bepresent in amounts greater than 0.0001 wt. %.

In one embodiment, the ethyl acetate concentration in the liquid stream113 may affect the first column reboiler duty and size. Decreasing ethylacetate concentrations may allow for reduced reboiler duty and size. Inone embodiment, to reduce the ethyl acetate concentration (a) thecatalyst in reactor may convert ethyl acetate in addition to aceticacid; (b) the catalyst may be less selective for ethyl acetate, and/or(c) the feed to reactor, including recycles, may contain less ethylacetate.

In the embodiment shown in FIG. 1, liquid stream 113 is introduced inthe upper part of first column 115, e.g., upper half or upper third. Inaddition to liquid stream 113, an extractive agent 116 and an ethylacetate recycle stream 117 are also fed to first column. Extractiveagent 116 is preferably introduced above liquid stream 113. Extractiveagent 116 may be heated from ambient temperature to a temperature of upto 70° C., e.g., up to 50° C., or up to 40° C. In another embodiment,Extractive agent 116 is not separately preheated, but is withdrawn fromsecond column 130, and cooled, if necessary, to a temperature of lessthan 70° C., e.g., less than 50° C., or less than 40° C., and directlyfed to first column 115. Depending on the ethyl acetate concentration ofethyl acetate recycle stream 117 this stream may be introduced above ornear the feed point of the liquid stream 113. Depending on the targetedethyl acetate concentration in the distillate of first column 115 thefeed point of ethyl acetate recycle stream 117 will vary.

Liquid stream 113 and ethyl acetate recycle stream 117 collectivelycomprise the organic feed to first column 115. In one embodiment, theorganic feed comprises from 1 to 25% of ethyl acetate recycle stream117, e.g., from 3% to 20% or from 5% to 15%, the remainder beingsupplied by liquid stream 113. This amount may vary depending on theproduction of reactor 103 and the amount of ethyl acetate to berecycled.

Extractive agent 116 preferably comprises water that has been retainedwithin the system. As described herein, extractive agent 116 may beobtained from a portion of the second residue. Extractive agent 116 maybe a dilute acid stream comprising up to 20 wt. % acetic acid, e.g., upto 10 wt. % acetic acid or up to 5 wt. % acetic acid. In one embodiment,the mass flow ratio of water in extractive agent 116 to the mass flow ofthe organic feed, which comprises liquid stream 113 and ethyl acetaterecycle stream 117, may range from 0.05:1 to 2:1, e.g., from 0.07 to0.9:1 or from 0.1:1 to 0.7:1. It is preferred that the mass flow ofextractive agent 116 is less than the mass flow of the organic feed.

In one embodiment, first column 115 is a tray column having from 5 to 90theoretical trays, e.g., from 10 to 60 theoretical trays or from 15 to50 theoretical trays. The number of actual trays for each column mayvary depending on the tray efficiency, which is typically from 0.5 to0.7 depending on the type of tray. The trays may be sieve trays, fixedvalve trays, movable valve trays, or any other suitable design known inthe art. In other embodiments, a packed column having structured packingor random packing may be employed.

When first column 115 is operated under 50 kPa, the temperature of theresidue exiting in line 118 preferably is from 20° C. to 100° C., e.g.,from 30° C. to 90° C. or from 40° C. to 80° C. The base of column 115may be maintained at a relatively low temperature by withdrawing aresidue stream comprising ethanol, ethyl acetate, water, and aceticacid, thereby providing an energy efficiency advantage. The temperatureof the distillate exiting in line 119 from column 115 preferably at 50kPa is from 10° C. to 80° C., e.g., from 20° C. to 70° C. or from 30° C.to 60° C. The pressure of first column 115 may range from 0.1 kPa to 510kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In someembodiments, first column 115 may operate under a vacuum of less than 70kPa, e.g., less than 50 kPa, or less than 20 kPa. Operating under avacuum may decrease the reboiler duty and reflux ratio of first column115. However, a decrease in operating pressure for first column 115 doesnot substantially affect column diameter.

In first column 115, a weight majority of the ethanol, water, aceticacid, are removed from the organic feed, including liquid stream 113 andethyl acetate recycle stream 117, and are withdrawn, preferablycontinuously, as residue in line 118. This includes any water added asan extractive agent 116. Concentrating the ethanol in the residuereduces the amount of ethanol that is recycled to reactor 103 and inturn reduces the size of reactor 103. Preferably less than 10% of theethanol from the organic feed, e.g., less than 5% or less than 1% of theethanol, is returned to reactor 103 from first column 115. In addition,concentrating the ethanol also will concentrate the water and/or aceticacid in the residue. In one embodiment, at least 90% of the ethanol fromthe organic feed is withdrawn in the residue, and more preferably atleast 95%. In addition, ethyl acetate may also be present in the firstresidue in line 118. The reboiler duty may decrease with an ethylacetate concentration increase in the first residue in line 118.

First column 115 also forms a distillate in line 119 that may becondensed and refluxed, for example, at a ratio from 30:1 to 1:30, e.g.,from 10:1 to 1:10 or from 5:1 to 1:5. Higher mass flow ratios of waterto organic feed may allow first column 115 to operate with a reducedreflux ratio.

The first distillate in line 119 preferably comprises a weight majorityof the acetaldehyde and ethyl acetate from liquid stream 113, as well asfrom ethyl acetate recycle stream 117. In one embodiment, the firstdistillate in line 119 comprises a concentration of ethyl acetate thatis less than the ethyl acetate concentration for the azeotrope of ethylacetate and water, and more preferably less than 75 wt. %.

In some embodiments, first distillate in stream 119 also comprisesethanol. Returning the ethanol may require an increase in reactorcapacity to maintain the same level of ethanol efficiency. To recoverethanol, the first distillate in line 119 may be fed, as is shown inFIG. 2, to an extraction column 120 to recover ethanol and reduce theamount of ethanol that is recycled to reactor 103. Extraction column 120may be a multi-stage extractor. As shown, the first distillate in line119 at least one extractant 121 are fed to extraction column 120. In oneembodiment, extractant 121 may comprise one or more of benzene,propylene glycol, or cyclohexane. Although water may be used, theextractant 121 preferably does not form an azeotrope with ethanol.Preferably, the extractant extracts ethanol from the first distillate inextract 122. The extractant may be recovered from extract 122 inrecovery column 123 and returned via line 124. The ethanol stream inline 125 may be combined with the ethanol product or returned to one ofthe distillation columns, such as first column 115. The raffinate 126may be returned to reaction zone 101. Preferably, raffinate 126, whichcomprises acetaldehyde and ethyl acetate, is deficient in ethanol withrespect to first distillate in line 119.

Exemplary components of the distillate and residue compositions forfirst column 115 are provided in Table 3 below. It should also beunderstood that the distillate and residue may also contain othercomponents, not listed in Table 3. For convenience, the distillate andresidue of the first column may also be referred to as the “firstdistillate” or “first residue.” The distillates or residues of the othercolumns may also be referred to with similar numeric modifiers (second,third, etc.) in order to distinguish them from one another, but suchmodifiers should not be construed as requiring any particular separationorder.

TABLE 3 EXTRACTIVE COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethyl Acetate   10 to 85 15 to 80 20 to 75 Acetaldehyde  0.1to 70 0.2 to 65  0.5 to 65  Acetal <3 0.01 to 2   0.05 to 1.5  Acetone<0.05 0.001 to 0.03   0.01 to 0.025 Ethanol <25 0.001 to 20   0.01 to15   Water  0.1 to 20  1 to 15  2 to 10 Acetic Acid <2 <0.1 <0.05Residue Acetic Acid  0.1 to 50 0.5 to 40   1 to 30 Water   20 to 85 25to 80 30 to 75 Ethanol   10 to 75 15 to 70 20 to 65 Ethyl Acetate 0.005to 30 0.03 to 25   0.08 to 1  

In one embodiment of the present invention, first column 115 may beoperated at a temperature where most of the water, ethanol, and aceticacid are removed into the residue stream and only a small amount ofethanol and water is collected in the distillate stream due to theformation of binary and tertiary azeotropes. The weight ratio of waterin the residue in line 118 to water in the distillate in line 119 may begreater than 1:1, e.g., greater than 2:1. The weight ratio of ethanol inthe residue to ethanol in the distillate may be greater than 1:1, e.g.,greater than 2:1.

The amount of acetic acid in the first residue may vary dependingprimarily on the conversion in reactor 103. In one embodiment, when theconversion is high, e.g., greater than 90%, the amount of acetic acid inthe first residue may be less than 10 wt. %, e.g., less than 5 wt. % orless than 2 wt. %. In other embodiments, when the conversion is lower,e.g., less than 90%, the amount of acetic acid in the first residue maybe greater than 10 wt. %.

The first distillate in line 119 preferably is substantially free ofacetic acid, e.g., comprising less than 1000 wppm, less than 500 wppm orless than 100 wppm acetic acid. The distillate may be purged from thesystem or recycled in whole or part to reactor 103. In some embodiments,when the distillate comprises ethyl acetate and acetaldehyde, thedistillate may be further separated, e.g., in a distillation column (notshown), into an acetaldehyde stream and an ethyl acetate stream. Theethyl acetate stream may also be hydrolyzed or reduced with hydrogen,via hydrogenolysis, to produce ethanol. Either of these streams may bereturned to reactor 103 or separated from system 100 as additionalproducts.

Some species, such as acetals, may decompose in first column 115 suchthat very low amounts, or even no detectable amounts, of acetals remainin the distillate or residue.

In addition, an equilibrium reaction between acetic acid/ethanol andethyl acetate may occur in the crude ethanol product after exitingreactor 103 or first column 115. Without being bound by theory, ethylacetate may be formed in the reboiler of first column 115. Depending onthe concentration of acetic acid in the crude ethanol product, thisequilibrium may be driven toward formation of ethyl acetate. Thisreaction may be regulated through the residence time and/or temperatureof the crude ethanol product.

In one embodiment, due to the composition of first residue in line 118the equilibrium may favor esterification to produce ethyl acetate. Whilethe esterification, either in the liquid or vapor phase, may consumeethanol, the esterification may also reduce the amount of acetic acidthat needs to be removed from the process. Ethyl acetate may be removedfrom first column 115 or from a second column 130. The esterificationmay be further promoted by passing a portion of the first residue inline 118 through an esterification reactor 127, as shown in FIG. 3. Theesterification reactor may be either a liquid or vapor phase reactor andmay comprise an acidic catalyst. A vapor phase reactor is preferred toconvert some of the first residue into an intermediate vapor feed 128 tobe introduced into the second column 130. Acid-catalyzed esterificationreactions may be used with some embodiments of the present invention.The catalyst should be thermally stable at reaction temperatures.Suitable catalysts may be solid acid catalysts comprising an ionexchange resin, zeolites, Lewis acid, metal oxides, inorganic salts andhydrates thereof, heteropoly acids, and salts thereof. Silica gel,aluminum oxide, and aluminum phosphate are also suitable catalysts. Acidcatalysts include, but are not limited to, sulfuric acid, and tosicacid. In addition, Lewis acids may also be used as esterificationcatalysts, such as scandium(III) or lanthanide(III) triflates,hafnium(IV) or zirconium(IV) salts, and diarylammonium arenesulfonates.The catalyst may also include sulfonated (sulphonic acid) ion-exchangeresins (e.g., gel-type and macroporous sulfonated styrene-divinylbenzene IERs), sulfonated polysiloxane resins, sulfonated perfluorinated(e.g., sulfonated poly-perfluoroethylene), or sulfonated zirconia.

To recover ethanol, first residue in line 118, or intermediate vaporfeed 128 in FIG. 3, may be further separated depending on theconcentration of acetic acid and/or ethyl acetate. In most embodimentsof the present invention, residue in line 118 is further separated in asecond column 130, also referred to as an “acid column.” Second column130 yields a second residue in line 131 comprising acetic acid and/orwater, and a vapor overhead in line 133 comprising ethanol and/or ethylacetate. In one embodiment, a weight majority of the water and/or aceticacid fed to second column 130 is removed in the second residue in line131, e.g., at least 60% of the water and/or acetic acid is removed asthe second residue in line 131 or more preferably at least 80% of thewater and/or acetic acid. An acid column may be desirable, for example,when the acetic acid concentration in the first residue is greater 50wppm, e.g., greater than 0.1 wt. %, 1 wt. %, e.g., greater than 5 wt. %.

In one embodiment, the first residue in line 118 may be preheated priorto being introduced into second column 130. The first residue in line118 may be heat integrated with either the residue of the second column130 or vapor overhead of second column 130. In some embodiments,esterification may be carried out in the vapor phase, as shown in FIG.3, which results in preheating a portion of the first residue in line118 to form an intermediate vapor feed 128. For purposes of the presentinvention, when preheating, it is preferred that less than 30 mol. % ofthe first residue in line 118 is in the vapor phase, e.g., less than 25mol. % or less than 20 mol. %. Greater vapor phase contents result inincreased energy consumption and a significant increase in the size ofsecond column 130. A portion of the first residue in line 129 mayby-pass esterification reactor 127 and be combined with the intermediatevapor feed 128 to maintain the necessary vapor mole fraction.

Esterifying the acetic acid in first residue in line 118 increases theethyl acetate concentration which leads to increases in the size ofsecond column 130 as well increases in reboiler duty. Thus, theconversion of acetic acid may be controlled depending on the initialethyl acetate concentration withdrawn from the first column. To maintainan efficient separation, the ethyl acetate concentration of the firstresidue in line 118 as it is fed to second column is preferably lessthan 1000 wppm, e.g., less than 800 wppm or less than 600 wppm.

Second column 130 concentrates the ethanol from the first residue suchthat a majority of the ethanol is carried overhead. Thus, the residue ofsecond column 130 may have an ethanol concentration of less than 5 wt.%, e.g. less than 1 wt. % or less than 0.5 wt. %. Lower ethanolconcentrations may be achieved without significant increases in reboilerduty or column size. Thus, in some embodiments it is efficient to reducethe ethanol concentration in the residue to less than 50 wppm, or morepreferably less than 25 wppm.

In FIG. 1, the first residue in line 118 is introduced to second column130, preferably in the top part of column 130, e.g., top half or topthird. Feeding the first residue in line 118 in a lower portion ofsecond column 130 may unnecessarily increase the energy requirements ofsecond column. Acid column 130 may be a tray column or packed column. InFIG. 1, second column 130 may be a tray column having from 10 to 110theoretical trays, e.g., from 15 to 95 theoretical trays or from 20 to75 theoretical trays. Additional trays may be used if necessary tofurther reduce the ethanol concentration in the residue. In oneembodiment, the reboiler duty and column size may be reduced byincreasing the number of trays.

Although the temperature and pressure of second column 130 may vary,when at atmospheric pressure the temperature of the second residue inline 131 preferably is from 95° C. to 160° C., e.g., from 100° C. to150° C. or from 110° C. to 145° C. In one embodiment, first residue inline 118 is preheated to a temperature that is within 20° C. of thetemperature of second residue in line 131, e.g., within 15° C. or within10° C. The temperature of the vapor overhead exiting in line 133 fromsecond column 130 preferably is from 50° C. to 120° C., e.g., from 75°C. to 118° C. or from 80° C. to 115° C. The temperature gradient may besharper in the base of second column 130.

The pressure of second column 130 may range from 0.1 kPa to 510 kPa,e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In one embodiment,second column 130 operates above atmospheric pressure, e.g., above 170kPa or above 375 kPa. Second column 130 may be constructed of a materialsuch as 316L SS, Allot 2205 or Hastelloy C, depending on the operatingpressure. The reboiler duty and column size for the second column remainrelatively constant until the ethanol concentration in the vaporoverhead in line 133 is greater than 90 wt. %.

As described herein, first column 115 is an extractive column thatpreferably uses water as the extractive agent. The additional water ispreferably separated in second column 130. While using water as anextractive agent may reduce the reboiler duty of first column 115, whenthe mass flow ratio of water to organic feed is greater than 0.65:1,e.g., greater than 0.6:1 or greater than 0.54:1, the additional watermay cause an increase in reboiler duty of second column 130 that offsetsany benefit gained by first column 115.

A portion of vapor overhead 133 may be withdrawn as a second distillatein line 132 that is condensed and refluxed, for example, at a ratio from12:1 to 1:12, e.g., from 10:1 to 1:10 or from 8:1 to 1:8. The vaporoverhead in line 133 preferably comprises 85 to 92 wt. % ethanol, e.g.,about 87 to 90 wt. % ethanol, with the remaining balance being primarilywater and ethyl acetate.

In one embodiment, water may be removed prior to recovering the ethanolproduct. Vapor overhead in line 133 may comprise less than 15 wt. %water, e.g., less than 10 wt. % water or less than 8 wt. % water. Asshown in FIG. 1, vapor overhead 133 may be fed to water separator 135,which may be an adsorption unit, membrane, molecular sieves, extractivecolumn distillation, or a combination thereof. In one embodiment, atleast 50% of the vapor overhead is fed to water separator 135, e.g., atleast 75% or at least 90%.

Water separator 135 in FIG. 1 may be a pressure swing adsorption (PSA)unit. For purposes of clarity the details of the PSA unit are not shownin the figures. The PSA unit is optionally operated at a temperaturefrom 30° C. to 160° C., e.g., from 80° C. to 140° C., and a pressurefrom 0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. The PSA unit maycomprise two to five beds. Water separator 135 may remove at least 95%of the water from vapor overhead 133, and more preferably from 95% to99.99% of the water from vapor overhead 133, into a water stream 134.All or a portion of water stream 134 may be returned to second column130 in line 136, which may increase the reboiler duty and/or size ofsecond column 130. Additionally or alternatively, all or a portion ofwater stream 134 may be purged via line 137. The remaining portion ofvapor overhead 133 exits the water separator 135 as ethanol mixturestream 138. In one embodiment, ethanol mixture stream 138 comprises morethan 92 wt. % ethanol, e.g., more than 95 wt. % or more than 99 wt. %.In one embodiment a portion of water stream 137 may be fed to firstcolumn 115 as the extractive agent.

A portion of vapor overhead 132 optionally may be mixed with ethanolmixture stream 138 and co-fed to light ends column 140 as shown by thehashed arrow in FIG. 1. This may be desired if additional water isneeded to improve separation in light ends column 140. It should beunderstood that reflux ratios may vary with the number of stages, feedlocations, column efficiency and/or feed composition. Operating with areflux ratio of greater than 3:1 may be less preferred because moreenergy may be required to operate second column 130.

Exemplary components for ethanol mixture stream 138 and residuecompositions for second column 130 are provided in Table 4 below. Itshould be understood that the distillate and residue may also containother components, not listed in Table 4. For example, in optionalembodiments, when ethyl acetate is in the feed to reactor 103, secondresidue in line 131, exemplified in Table 4, may also comprise highboiling point components.

TABLE 4 ACID COLUMN Conc. Conc. Conc. (wt. %) (wt. %) (wt. %) EthanolMixture Stream Ethanol   90 to 99.9 92 to 99 96 to 99 Ethyl Acetate <100.001 to 5    0.005 to 4    Acetaldehyde <10 0.001 to 5    0.005 to 4   Water <10 0.001 to 3    0.01 to 1   Acetal <2 0.001 to 1    0.005 to0.5  Second Residue Acetic Acid 0.1 to 45  0.2 to 40  0.5 to 35  Water 45 to 100   55 to 99.8   65 to 99.5 Ethyl Acetate <0.1 0.0001 to 0.05 0.0001 to 0.01  Ethanol <5 0.002 to 1    0.005 to 0.5 

The weight ratio of ethanol in the ethanol mixture stream 138 to ethanolin the second residue in line 131 preferably is at least 35:1.Preferably, ethanol mixture stream 138 is substantially free of aceticacid and may contain, if any, trace amounts of acetic acid.

In one embodiment, ethyl acetate fed to second column 130 mayconcentrate in the vapor overhead and pass through with ethanol mixturestream 138. Thus, preferably no ethyl acetate is withdrawn in the secondresidue in line 131. Advantageously, this allows most of the ethylacetate to be subsequently recovered without having to further processthe second residue in line 131.

In optional embodiments, the feed to reactor 103 may comprise aceticacid and/or ethyl acetate. When ethyl acetate is used alone as a feed,the crude ethanol product may comprise substantially no water and/oracetic acid. There may be high boiling point components, such asalcohols having more than 2 carbon atoms, e.g., n-propanol, isopropanol,n-butanol, 2-butanol, and mixtures thereof. High boiling pointcomponents refer to compounds having a boiling point that is greaterthan ethanol. The high boiling point components may be removed in secondcolumn 130 in the second residue in line 131.

In one embodiment, due to the presence of ethyl acetate in ethanolmixture stream 138, an additional third column 140 may be used tofurther purify the ethanol. A third column 140, referred to as a “lightends” column, is used for removing ethyl acetate from ethanol mixturestream 138 and producing an ethanol product in the third residue in line141. Light ends column 140 may be a tray column or packed column. InFIG. 1, third column 140 may be a tray column having from 5 to 90theoretical trays, e.g., from 10 to 60 theoretical trays or from 15 to50 theoretical trays.

The feed location of ethanol mixture stream 138 may vary depending onethyl acetate concentration, but it is preferred to feed ethanol mixturestream 138 to the upper portion of third column 140. Higherconcentrations of ethyl acetate may be fed at a higher location in thirdcolumn 140. The feed location should avoid the very top trays, near thereflux, to avoid excess reboiler duty requirements for the column and anincrease in column size. For example, in a column having 45 actualtrays, the feed location should between 10 to 15 trays from the top.Feeding at a point above this may increase the reboiler duty and size oflight ends column 140.

Ethanol mixture stream 138 may be fed to third column 140 at atemperature of up to 70° C., e.g., up to 50° C., or up to 40° C. In someembodiments it is not necessary to further preheat ethanol mixturestream 138.

Ethyl acetate may be concentrated in the third distillate in line 142.Due to the relatively lower amounts of ethyl acetate fed to third column140, the third distillate in line 142 may also comprise substantialamounts of ethanol. To recover the ethanol, the third distillate in line142 may be fed to the first column as ethyl acetate recycle stream 117.Because this increases the demands on the first and second columns, itis preferred that the concentration of ethanol in the third distillatein line 142 be from 70 to 90 wt. %, e.g., from 72 to 88 wt. %, or from75 to 85 wt. %.

In other embodiments, a portion of the third distillate in line 142 maybe purged from the system in line 143 as a separate product, such as anethyl acetate solvent.

In some embodiments, the ethanol may be recovered using an extractivecolumn 145 as shown in FIG. 4. Extraction column 145 may be amulti-stage extractor. In extraction column 145, the third distillate inline 142 is fed along with at least one extractive agent 146. In oneembodiment, the extractive agent may be benzene, propylene glycol, andcyclohexane. Although water may be used, the extractive agent preferablydoes not form an azeotrope with ethanol. Preferably, the extractiveagent extracts ethanol from the third distillate in extract 147. Theextractive agent may be recovered in recovery column 148 and returnedvia line 149. The ethanol stream in line 150 may be combined with thethird residue in line 141. The raffinate 151, which comprises ethylacetate, may be returned to reaction zone 101 or optionally to firstcolumn 115 as ethyl acetate recycle stream 117. Preferably, raffinate151 is deficient in ethanol with respect to third distillate in line142.

In some embodiment, the third residue in line 141 may comprises lessthan 8 wt. % water, e.g., less than 3 wt. % water or less than 0.5 wt. %water. In an optional embodiment, the third residue may be furtherprocessed to recover ethanol with a desired amount of water, forexample, using a further distillation column, adsorption unit, membraneor combination thereof. The reduced water concentration may be less than3 wt. % water, e.g., less than 0.5 wt. % water or less than 0.1 wt. %water. In most embodiments, the water is removed prior to entering thirdcolumn 140 using water separator 135 and thus further drying of theethanol is not required.

Third column 140 is preferably a tray column as described above andpreferably operates at atmospheric pressure. The temperature of thethird residue in line 141 exiting from third column 140 preferably isfrom 65° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C. to80° C. The temperature of the third distillate in line 142 exiting fromthird column 140 preferably is from 30° C. to 70° C., e.g., from 40° C.to 65° C. or from 50° C. to 65° C.

The pressure of third column 140 may range from 0.1 kPa to 510 kPa,e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In someembodiments, third column 140 may operate under a vacuum of less than 70kPa, e.g., less than 50 kPa, or less than 20 kPa. Decreasing operatingpressure substantially decreases column diameter and reboiler duty forthird column 140.

Exemplary components for the ethanol mixture stream and the residuecompositions for third column 140 are provided in Table 5 below. Itshould be understood that the distillate and residue may also containother components, not listed in Table 5.

TABLE 5 LIGHT ENDS COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Third Distillate Ethanol 70 to 99 72 to 95 75 to 90 Ethyl Acetate  1 to30  1 to 25  1 to 15 Acetaldehyde <15 0.001 to 10   0.1 to 5   Water <100.001 to 2    0.01 to 1   Acetal <2 0.001 to 1    0.01 to 0.5  ThirdResidue Ethanol   80 to 99.5 85 to 97 90 to 95 Water <8 0.001 to 3   0.01 to 1   Ethyl Acetate <1.5 0.0001 to 1    0.001 to 0.5  Acetic Acid<0.5 <0.01 0.0001 to 0.01 

When the first residue in line 118 comprises low amounts of acetic acidand/or there is no esterification within first residue, such that theethyl acetate concentration is less than 50 wppm, third column 140 maybe optional and removed as shown in FIG. 5. Thus, ethanol mixture stream138 from the water separator 135 may be the ethanol product and no ethylacetate recycle stream is required.

Depending on the amount of water and acetic acid contained in the secondresidue it may be desired to treat the second residue in line 131 in oneor more of the following processes. A suitable weak acid recovery systemis described in US Pub. No. 2012/0010446, the entire contents anddisclosure of which is hereby incorporated by reference. When the secondresidue comprises primarily acetic acid, e.g., greater than 70 wt. %,the residue may be recycled to the reactor without any separation of thewater. When the second residue comprises from 50 to 70 wt. % aceticacid, the second residue may be separated into an acetic acid stream anda water stream. Acetic acid may also be recovered in some embodimentsfrom the first residue. The residue may be separated into the aceticacid and water streams by a distillation column or one or moremembranes. If a membrane or an array of membranes is employed toseparate the acetic acid from the water, the membrane or array ofmembranes may be selected from any suitable acid resistant membrane thatis capable of removing a permeate water stream. The resulting aceticacid stream optionally is returned to reactor 103. The resulting waterstream may be used as an extractive agent or to hydrolyze anester-containing stream in a hydrolysis unit.

In other embodiments, for example where the second residue in line 131comprises less than 50 wt. % acetic acid, possible options include oneor more of: (i) returning a portion of the residue to reactor 103, (ii)neutralizing the acetic acid, (iii) reacting the acetic acid with analcohol, or (iv) disposing of the residue in a waste water treatmentfacility. It also may be possible to separate a residue comprising lessthan 50 wt. % acetic acid using a weak acid recovery distillation columnto which a solvent (optionally acting as an azeotroping agent) may beadded. Exemplary solvents that may be suitable for this purpose includeethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, vinylacetate, diisopropyl ether, carbon disulfide, tetrahydrofuran,isopropanol, ethanol, and C₃-C₁₂ alkanes. When neutralizing the aceticacid, it is preferred that the residue in line 131 comprises less than10 wt. % acetic acid. Acetic acid may be neutralized with any suitablealkali or alkaline earth metal base, such as sodium hydroxide orpotassium hydroxide. When reacting acetic acid with an alcohol, it ispreferred that the residue comprises less than 50 wt. % acetic acid. Thealcohol may be any suitable alcohol, such as methanol, ethanol,propanol, butanol, or mixtures thereof. The reaction forms an ester thatmay be integrated with other systems, such as carbonylation productionor an ester production process. Preferably, the alcohol comprisesethanol and the resulting ester comprises ethyl acetate. Optionally, theresulting ester may be fed to the hydrogenation reactor.

In some embodiments, when the second residue in line 131 comprises veryminor amounts of acetic acid, e.g., less than 5 wt. % or less than 1 wt.%, the residue may be neutralized and/or diluted before being disposedof to a waste water treatment facility. The organic content, e.g.,acetic acid content, of the residue beneficially may be suitable to feedmicroorganisms used in a waste water treatment facility.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in the figures. Heat may besupplied to the base of each column or to a circulating bottom streamthrough a heat exchanger or reboiler. Other types of reboilers, such asinternal reboilers, may also be used. The heat that is provided to thereboilers may be derived from any heat generated during the process thatis integrated with the reboilers or from an external source such asanother heat generating chemical process or a boiler. Although onereactor and one flasher are shown in the figures, additional reactors,flashers, condensers, heating elements, and other components may be usedin various embodiments of the present invention. As will be recognizedby those skilled in the art, various condensers, pumps, compressors,reboilers, drums, valves, connectors, separation vessels, etc., normallyemployed in carrying out chemical processes may also be combined andemployed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary.Temperatures within the various zones will normally range between theboiling points of the composition removed as the distillate and thecomposition removed as the residue. As will be recognized by thoseskilled in the art, the temperature at a given location in an operatingdistillation column is dependent on the composition of the material atthat location and the pressure of column. In addition, feed rates mayvary depending on the size of the production process and, if described,may be generically referred to in terms of feed weight ratios.

The ethanol product produced by the processes of the present inventionmay be an industrial grade ethanol or fuel grade ethanol. Exemplaryfinished ethanol compositional ranges are provided below in Table 6.

TABLE 6 FINISHED ETHANOL COMPOSITIONS Component Conc. (wt. %) Conc. (wt.%) Conc. (wt. %) Ethanol   85 to 99.9   90 to 99.5   92 to 99.5 Water<12 0.1 to 9   0.5 to 8   Acetic Acid <1 <0.1 <0.01 Ethyl Acetate <2<0.5 <0.05 Acetal <0.05 <0.01 <0.005 Acetone <0.05 <0.01 <0.005Isopropanol <0.5 <0.1 <0.05 n-propanol <0.5 <0.1 <0.05

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment,the finished ethanol composition is substantially free of acetaldehyde,optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5wppm or less than 1 wppm.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingapplications as fuels, solvents, chemical feedstocks, pharmaceuticalproducts, cleansers, sanitizers, hydrogen transport or consumption. Infuel applications, the finished ethanol composition may be blended withgasoline for motor vehicles such as automobiles, boats and small pistonengine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, aldehydes, and higheralcohols, especially butanol. In the production of ethyl acetate, thefinished ethanol composition may be esterified with acetic acid. Inanother application, the finished ethanol composition may be dehydratedto produce ethylene.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In addition, it should be understood that aspectsof the invention and portions of various embodiments and variousfeatures recited herein and/or in the appended claims may be combined orinterchanged either in whole or in part. In the foregoing descriptionsof the various embodiments, those embodiments which refer to anotherembodiment may be appropriately combined with one or more otherembodiments, as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

1-20. (canceled)
 21. A process for producing ethanol comprising:hydrogenating acetic acid and/or an ester thereof in a reactor in thepresence of a catalyst to form a crude ethanol product; separating aportion of the crude ethanol product in a first extractive distillationcolumn to yield a first distillate comprising acetaldehyde and ethylacetate, and a first residue comprising ethanol, and water; separating aportion of the first residue in a second distillation column to yield asecond residue comprising water and a vapor overhead comprising ethanoland water; removing water from a portion of the vapor overhead to yieldan ethanol mixture stream; and separating at least a portion of theethanol mixture stream in a third distillation column to yield a thirddistillate comprising 70 to 90 wt. % ethanol and a third residuecomprising ethanol and less than 8 wt. % water; wherein the thirddistillate is fed to the first column and at least a portion of thefirst distillate is returned to the reactor.
 22. The process of claim21, further comprising introducing an extractive agent to the firstcolumn.
 23. The process of claim 22, wherein the extractive agentcomprises water.
 24. The process of claim 22, wherein the extractiveagent is derived from a portion of the second residue.
 25. The processof claim 22, wherein the extractive agent is derived from the waterremoved from the portion of the vapor overhead.
 26. The process of claim21, wherein the first residue comprises from 50 to 99.9% of the ethanolfrom the crude ethanol product.
 27. The process of claim 21, wherein thefirst residue comprises from 80 to 100% of the water from the crudeethanol product.
 28. The process of claim 21, wherein the first residuecomprises from 85 to 100% of the acetic acid from the crude ethanolproduct.
 29. The process of claim 21, wherein the first distillatefurther comprises at least one component selected from the groupconsisting of diethyl acetal, acetone and ethyl acetate.
 30. The processof claim 21, further comprising: separating the crude ethanol product ina separator to form a liquid stream comprising ethanol and a vaporstream comprising hydrogen.
 31. The process of claim 30, wherein theseparator comprises one or more membranes.
 32. The process of claim 30,wherein the separator comprises a flasher or a knock out pot.
 33. Theprocess of claim 21, wherein the first distillate is separated with anextractant in an extractive distillation column to form an extractcomprising ethanol and a raffinate comprising acetaldehyde, and furtherwherein the raffinate is returned to the reactor.
 34. The process ofclaim 33, wherein the extractant comprises one or more of benzene,propylene glycol or cyclohexane.
 35. The process of claim 33, whereinthe extractant comprises water.
 36. The process of claim 33, wherein theextract is combined with either the third residue, the seconddistillate, or the first residue.
 37. A process for purifying a streamto yield ethanol comprising: providing an ethanol mixture streamcomprising from 90 to 99.9 wt. % ethanol, 0.0001 to 10 wt. % ethylacetate, 0.0001 to 10 wt. % acetaldehyde, 0.0001 to 10 wt. % water,0.0001 to 10 wt. % acetal, separating the ethanol mixture stream in adistillation column to concentrate ethyl acetate in the distillate andrecover ethanol in the residue, wherein the distillate comprises from 70to 99 wt. % ethanol and the residue comprises from 80 to 99.5 wt. %ethanol.
 38. The process of claim 37, further comprising separating thedistillate with an extractant in an extractive distillation column toform an extract comprising ethanol and a raffinate comprising ethylacetate.
 39. The process of claim 38, wherein the extract is combinedwith the residue.
 40. The process of claim 37, wherein the distillatecomprises from 1 to 30 wt. % ethyl acetate.